1. Field of the Invention
The present invention relates to an endless rectilinear motion guide unit, wherein a pair of lower and upper load-carrying trackways are formed on each side of a track rail member, viz., four trackways in all on both sides thereof and, on the inner sidewall of a slide unit are also formed the corresponding number of lower and upper load-carrying trackways for mating in position with said four load-carrying trackways of the track rail member, so that the slide unit, upon having been assembled in straddling relation with said track rail member with a plurality of cylindrical rollers being arranged in parallel with one another between the mating trackways, can freely and rectilinearly move on said track rail member.
In more details, the present invention provides an endless rectilinear motion guide unit wherein two endless circulation passages are provided in each of the opposing sides of the slide unit, which are so arranged, as seen in a cross section thereof, that their longitudinal axes cross each other at right angles, while the longitudinal lengths of the two endless circulation passages differ from each other such that the longer circulation passage encompasses the shorter circulation passage within the loop, but the lengths of the load-carrying trackway surfaces of said two circulation passages are the same.
2. Prior Arts
German utility model application No. 1971845 and Japanese patent application publication No. 24646-1987 each disclose an endless rectilinear motion guide unit having four trackways along and through which a plurality of parallel-arranged cylindrical rollers move.
However, the prior units have the following inherent disadvantages:
In case of the German utility model, for example, two endless circulation passages are formed on each side of the slide unit, which are so arranged that one encompasses the other but due to the difference in length of the two passages, load capacities thereof differ from each other as the result with the shorter one having shorter effective life, so that the prior art unit can find only limited utility.
Furthermore, in case of the Japanese patent application, two endless circulation passages are provided in each of the opposing sides of the slide unit, which are linked each other like a chain so that through the load-carrying trackways of the two passages are the same in length, the longitudinal length as a whole of the associated endless circulation passages becomes greater, inevitably resulting in an enlargement of the unit as a whole.